Mining Powers Modern Life, but Can Leave Scarred Lands and Polluted Waters Behind
By Matthew Ross
Modern society relies on metals like copper, gold and nickel for uses ranging from medicine to electronics. Most of these elements are rare in Earth's crust, so mining them requires displacing vast volumes of dirt and rock. Hard rock mining – so called because it refers to excavating hard minerals, not softer materials like coal or tar sands – generated $600 billion in revenues worldwide in 2017.
The Trump administration has revived several controversial mining proposals that previously were blocked or stalemated. They include the Pebble Mine at the headwaters of Alaska's Bristol Bay and leasing around Minnesota's Boundary Waters Canoe Area Wilderness. It also approved a large copper mine in southern Arizona, which was subsequently blocked by a federal court ruling.
I study human-altered landscapes, including areas impacted by mines. Mining operations are major water pollution sources and can cause problems that persist for generations. Their global footprints also directly reshape significant portions of Earth's topography, leaving indelible evidence of human presence.
Digging Deep and Wide
In most locations, concentrations of copper, gold and other elements are too low to be extracted profitably. But in some spots they occur in seams of mineable, high-concentration minerals called ores. The economically viable concentration of a mineral depends largely on its market price. Gold ore can be viable at concentrations as low as 0.0001%, while copper becomes uneconomic below 0.5%.
To reach these deposits underground, miners tunnel, dig open pits or scrape through the earth's surface. The choice of technique depends on factors including how consolidated the ore is, the geologic setting and the depth of the ore.
Deep mines disturb the smallest amount of surface land, but are inherently more dangerous for miners. Far below the earth's surface, crews constantly risk encountering toxic gas fumes or stale air with no life-giving oxygen. Other dangers include earthquakes and equipment failures. In 2010, 33 Chilean miners spent over two months trapped underground in a copper-gold mine after a ramp collapsed, but ultimately were rescued.
Growing international emphasis on mine safety and changes in technology and ore quality have prompted a shift from deep mining to pit mines or surface mines, which access ores from the open air. Pit mines can be up to three-quarters of a mile deep, but typically cover less than 20 square miles. In contrast, surface mines typically extend less than 1,000 feet into the earth's crust, but can extend over hundreds of square miles.
Along with metals such as gold, silver and iron, mines also produce materials including sand and gravel, crushed stone and Portland cement. USGS
Accessing ore typically involves blowing apart bedrock, removing it from the shaft or pit and storing waste materials nearby after extracting the ore. In these heaps of loose rock, known as spoil piles, previously buried raw minerals are exposed to air or water. Sulfur-rich compounds in the rock react with oxygen and water, producing sulfuric acid, which can lower the pH of nearby streams to levels comparable to lemon juice or vinegar.
At its worst this process, known as acid mine drainage, can kill most native aquatic life. If acid drainage reaches groundwater, it may persist for decades or centuries and start a cascade of other impacts that impair water quality throughout local river networks.
When acid mine drainage lowers a stream's pH, other metals can also start to melt out of minerals in spoil piles, mine shafts or adjacent soils, leaching into soil and groundwater that intersects these areas. This creates waters with increased levels of cadmium, copper, lead and other heavy metals, which are harmful to aquatic insects, fish and human health.
These effects can be transported far downstream and last for generations. Old and abandoned mines around the world have harmed water quality long after mining has ceased. Their impacts can come as long-term slow leakage, or as sudden discharges like the 2015 Gold King spill near Silverton, Colorado, which released three million gallons of mine wastewater and debris into the Animas River.
According to the U.S. Government Accountability Office, there are at least 161,000 abandoned hardrock mining sites in the U.S. West and Alaska. Of these, at least 33,000 have contaminated water supplies or left piles of mine waste contaminated with arsenic behind.
Altering the Planet's Shape
Mining operations have also left thousands of square miles of land altered. In some cases, particularly mountaintop removal mining, entire land forms are permanently reshaped. For millennia the planet's surface was configured by the slow geologic processes of wind and rain. In contrast, mining alters the very geology, topography, hydrology and ecology of sites within years or decades.
These earth-moving activities represent the kind of effect that has led many environmental scientists to argue that our planet has entered a new geologic epoch – the Anthropocene – where human choices have a greater impact on the earth than purely natural processes. Landscape evolution moves in very slow cycles, so these topographic and geologic impacts may last far longer than mining's effects on water quality. And because geologic processes are slow, scientists don't know how these landscapes will diverge or converge in their future evolution.
Essential and Scarce
Like oil and gas producers, mining companies have to contend with the fact that the products they seek are scarce, and easily extractable pools have already been tapped, leading to decreases in ore quality. But demand for these metals continues to grow.
Rapidly expanding green energy will require extracting vast quantities of rare earth metals to power wind turbines, electric vehicle batteries and solar panels. Cellphones, computers, camera lenses and other goods also contain these materials.
Economic imperatives lead companies to continue to push for new mines, either in the U.S. or abroad, where environmental controls may be weaker. And new projects are likely to move more rock, consume more energy and have longer-lasting impacts than those that preceded them.
Ensuring that mining operations are subject to effective oversight and long-term monitoring, and that companies are held accountable for environmental damages, is a long-term challenge wherever mining takes place. The best way to completely avoid the complications that come from mining more minerals is to reduce consumption of them, make mining processes more efficient and make it more economic to recycle industrial materials and rare earth metals.
Matthew Ross is an assistant professor of water quality at Colorado State University.
Disclosure statement: Matthew Ross receives funding from the National Science Foundation and NASA.
Reposted with permission from our media associate The Conversation.
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The ghoulishly named ogre-faced spider can "hear" with its legs and use that ability to catch insects flying behind it, the study published in Current Biology Thursday concluded.
"Spiders are sensitive to airborne sound," Cornell professor emeritus Dr. Charles Walcott, who was not involved with the study, told the Cornell Chronicle. "That's the big message really."
The net-casting, ogre-faced spider (Deinopis spinosa) has a unique hunting strategy, as study coauthor Cornell University postdoctoral researcher Jay Stafstrom explained in a video.
They hunt only at night using a special kind of web: an A-shaped frame made from non-sticky silk that supports a fuzzy rectangle that they hold with their front forelegs and use to trap prey.
They do this in two ways. In a maneuver called a "forward strike," they pounce down on prey moving beneath them on the ground. This is enabled by their large eyes — the biggest of any spider. These eyes give them 2,000 times the night vision that we have, Science explained.
But the spiders can also perform a move called the "backward strike," Stafstrom explained, in which they reach their legs behind them and catch insects flying through the air.
"So here comes a flying bug and somehow the spider gets information on the sound direction and its distance. The spiders time the 200-millisecond leap if the fly is within its capture zone – much like an over-the-shoulder catch. The spider gets its prey. They're accurate," coauthor Ronald Hoy, the D & D Joslovitz Merksamer Professor in the Department of Neurobiology and Behavior in the College of Arts and Sciences, told the Cornell Chronicle.
What the researchers wanted to understand was how the spiders could tell what was moving behind them when they have no ears.
It isn't a question of peripheral vision. In a 2016 study, the same team blindfolded the spiders and sent them out to hunt, Science explained. This prevented the spiders from making their forward strikes, but they were still able to catch prey using the backwards strike. The researchers thought the spiders were "hearing" their prey with the sensors on the tips of their legs. All spiders have these sensors, but scientists had previously thought they were only able to detect vibrations through surfaces, not sounds in the air.
To test how well the ogre-faced spiders could actually hear, the researchers conducted a two-part experiment.
First, they inserted electrodes into removed spider legs and into the brains of intact spiders. They put the spiders and the legs into a vibration-proof booth and played sounds from two meters (approximately 6.5 feet) away. The spiders and the legs responded to sounds from 100 hertz to 10,000 hertz.
Next, they played the five sounds that had triggered the biggest response to 25 spiders in the wild and 51 spiders in the lab. More than half the spiders did the "backward strike" move when they heard sounds that have a lower frequency similar to insect wing beats. When the higher frequency sounds were played, the spiders did not move. This suggests the higher frequencies may mimic the sounds of predators like birds.
University of Cincinnati spider behavioral ecologist George Uetz told Science that the results were a "surprise" that indicated science has much to learn about spiders as a whole. Because all spiders have these receptors on their legs, it is possible that all spiders can hear. This theory was first put forward by Walcott 60 years ago, but was dismissed at the time, according to the Cornell Chronicle. But studies of other spiders have turned up further evidence since. A 2016 study found that a kind of jumping spider can pick up sonic vibrations in the air.
"We don't know diddly about spiders," Uetz told Science. "They are much more complex than people ever thought they were."
Learning more provides scientists with an opportunity to study their sensory abilities in order to improve technology like bio-sensors, directional microphones and visual processing algorithms, Stafstrom told CNN.
"The point is any understudied, underappreciated group has fascinating lives, even a yucky spider, and we can learn something from it," he told CNN.
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